1. Technical Field
The present invention relates to a voltage controlled oscillator, a receiver, and a communication device. In particular, the present invention is preferably applied to a voltage controlled oscillator in which a surface acoustic wave element is used as a resonator to form a feedback circuit.
2. Prior Art
Conventional high frequency oscillators include voltage controlled oscillators in which micro strip lines and strip lines are used as a resonator. Unlike a surface acoustic wave element that uses the piezoelectric effect of a quartz crystal substrate, the voltage controlled oscillator using such a resonator can not expect to have a large Q value.
On the other hand, the voltage controlled oscillator using a surface acoustic wave element as a resonator is able to have highly stable and high quality properties and, thus, it may be used as a reference oscillator for communication networks with a transmission rate of several gigabits/s or more. This type of voltage controlled oscillator is described, for instance, in Japan Laid-Open Patent Application 59-158106.
FIG. 11 is a block diagram showing an exemplary structure of the prior art voltage controlled oscillator. A surface acoustic wave element 201 and a 3 dBxe2x88x9290xc2x0 coupler having an additional control part for changing the phase value within the oscillation loop with control voltage Vc supplied from an external source are interposed in series to form the feedback circuit of an amplifier 202 for oscillation. Here, the control voltage Vc is supplied to the 3 dBxe2x88x9290xc2x0 coupler 203 to change the phase value within the oscillation loop and, thus, to change the oscillation frequency.
A voltage controlled oscillator having an output power divider besides the structure in FIG. 11 is described in the journal of IEEE International Frequency Control Symposium, pp519-527, 1998.
FIG. 12 is a block diagram to show the structure of this prior art voltage controlled oscillator.
FIG. 12 shows a surface acoustic wave element 301, a variable phase shifter 302 for changing the phase value within the oscillation loop with control voltage supplied from an external source, an amplifier 303, an equal power divider 304 for equally distributing the output from the oscillation loop and supplying it outside, and a loop adjustment line 305. The surface acoustic wave element 301, variable phase shifter 302, equal power divider 304, and loop adjustment line 305 are interposed in series to form a feedback loop on the output and input sides of the amplifier 303.
The loop adjustment line 305 is provided with a transmission line formed by a microstrip line. With fine adjustment of the line length, frequency regulation can be executed to make the phase angle zero after one round of the feedback loop.
However, the prior art voltage controlled oscillators described above have many structural elements and, therefore, require a proportionally large number of parts. This can cause problems in reliability and increased cost. In particular, the voltage controlled oscillator in FIG. 12 requires many parts and a large mounting surface area for the variable phase shifter 302 and equal power divider 304.
For the voltage controlled oscillator with an output frequency of several hundred MHz, the variable phase shifter 302 and equal power divider 304 can consist of a lumped constant circuit, which allows a reduction in the size of the entire circuit, but requires many parts. For a voltage controlled oscillator with an output frequency of several GHz, the variable phase shifter 302 and equal power divider 304 can consist of a transmission line designed with distributed constants, which allows a reduced number of parts, but requires large mounting surfaces due to the length and size of the transmission line.
One purpose of the present invention is to provide a voltage controlled oscillator, a receiver, and a communication device, which have a reduced mounting area for downsizing while satisfying the basic properties.
To solve the problems described above, the voltage controlled oscillator, according to one embodiment of the invention, is characterized by comprising an amplifier; a surface acoustic wave element for forming a feedback circuit for the amplifier; a phase adjustment circuit consisting of a filter and interposed in the feedback circuit; a phase shifter consisting of a hybrid coupler to which an additional control part is attached for changing the phase value within the oscillation loop with control voltage supplied from an external source; an equal power divider for equally distributing output power within the oscillation loop and supplying it outside the oscillation loop; and a multi-layer board for mounting the amplifier, surface acoustic wave element, phase adjustment circuit, phase shifter, and equal power divider in at least two separate layers.
This prevents extension of the mounting area and allows a larger variable range of frequencies for the voltage controlled oscillator while obtaining excellent frequency properties for the control voltage.
The mounting area can be reduced for downsizing the voltage controlled oscillator in both forms of a lumped constant circuit and a distributed constant circuit.
Furthermore, a low insertion loss and low return loss are realized, which allows for minimized circuit loss and reduced output fluctuation, thus ensuring stable circuit operation for the load.
The voltage controlled oscillator, according to another embodiment the invention, is characterized by the multi-layer board and is provided with a microstrip line structure consisting of a first wiring layer and a second wiring layer, and a strip line structure consisting of the second wiring layer, a third wiring layer, and a fourth wiring layer.
This allows stacking of the strip line and microstrip line structures for the purpose of downsizing as well as allowing a via connection between the strip line and microstrip line structures, which ensures efficient circuit geometry. A distributed constant circuit, which requires a large horizontal mounting area, can be stacked vertically for the purpose of downsizing, thereby significantly reducing the mounting area.
The underlying strip line structure contributes to more ground layers and improved mechanical strength of the circuit board. The circuit board can be connected to and mounted on a main board through the ground layers. The voltage controlled oscillator according to another embodiment of the invention is characterized by the second and fourth wiring layers having a ground layer.
This allows the strip line structure to share the ground layer with the microstrip line structure. A wiring layer can be added to the strip line structure to stack the microstrip line structure on the strip line structure. This prevents an increase in the number of wiring layers and enables the provision of the microstrip line and strip line structures on the same board.
The voltage controlled oscillator according to another embodiment of the invention is characterized by the amplifier, surface acoustic wave element, additional control part, and phase adjustment circuit being provided on the micro strip line structure; and the hybrid coupler and equal power divider being provided on the strip line structure. This allows surface mounting of parts that can not be built in the board, such as a surface acoustic wave element for the voltage controlled oscillator in the form of a distributed constant circuit as well as realizes a multi-layered transmission line, which occupies a large area. The voltage controlled oscillator can satisfy the basic properties while being downsized.
The voltage controlled oscillator according to another embodiment of the invention is characterized by the hybrid coupler and equal power divider provided on the strip line structure having a transmission line which is rectangularly bent.
This prevents a horizontal extension of the transmission line that is provided on the strip line structure, realizing a downsized voltage controlled oscillator.
The voltage controlled oscillator according to another embodiment of the invention is characterized by engaging the convex rectangular bends in the concave rectangular bends. This allows for efficient usage of the board area by simply changing the transmission line pattern. The mounting board can be downsized even if the transmission line is horizontally disposed in the board.
The voltage controlled oscillator according to another embodiment of the invention is characterized by the multi-layer board and is provided with a micro strip line structure consisting of a first wiring layer and a second wiring layer; a strip line structure consisting of the second wiring layer, a third wiring layer, and a fourth wiring layer; and a micro strip line structure consisting of the fourth wiring layer and a fifth wiring layer.
This allows stacking of a microstrip line structure above and below the strip line structure by adding the fifth wiring layer. This also allows a via connection between the strip line and microstrip line structures for efficient circuit geometry, enlarging the mounting surface area while preventing the increase in size of the circuit board.
The voltage controlled oscillator according to another embodiment of the invention is characterized by the second and fourth wiring layers having a ground layer. This allows the sharing of the ground layers above and below the center strip line structure with the micro strip line structures provided above and below them.
A microstrip line structure can be stacked one each above and below the strip line structure by adding a wiring layer one each above and below the strip line structure. This realizes two layers of microstrip line structures and one layer of strip line structure on the same board while preventing the increase in number of the wiring layers.
The voltage controlled oscillator according to another embodiment of the invention is characterized by the multi-layer board and is provided with a micro strip line structure consisting of a first wiring layer and a second wiring layer; a strip line structure consisting of the second wiring layer, a third wiring layer, and a fourth wiring layer; and a strip line structure consisting of the fourth wiring layer, a fifth wiring layer, and a sixth wiring layer.
This allows the stacking of microstrip line and strip line structures above and below the strip line structure, respectively, using only six wiring layers. The strip line and microstrip line structures can be via connected for efficient circuit geometry. This prevents the increase in the mounting area and realizes a downsized circuit board even for a large scale voltage controlled oscillator in the form of a distributed constant circuit.
The voltage controlled oscillator according to another embodiment of the invention is characterized by the second, fourth, and sixth wiring layers having a ground layer. This allows the sharing of the ground layers above and below the center strip line structure with the micro strip line and strip line structures provided above and below them.
A microstrip line structure and a strip line structure can be stacked above and below the strip line structure, respectively, by adding a wiring layer above the strip line structure and two wiring layers below the strip line structure. The receiver according to the invention comprises a photodiode for converting optical signals into electric signals; a clock data recovery for extracting data and synchronous signals from the electric signals; a voltage controlled oscillator for providing signals to operate the clock data recovery; a deserializer for converting serial data that are extracted by the clock data recovery into parallel data; and a decoder for decoding the parallel data, characterized by the voltage controlled oscillator comprising an amplifier; a surface acoustic wave element for forming a feedback circuit for the amplifier; a phase adjustment circuit consisting of a filter and interposed in the feedback circuit; a phase shifter consisting of a hybrid coupler to which an additional control part is attached for changing the phase value within the oscillation loop with control voltage supplied from an external source; an equal power divider for equally distributing output power within the oscillation loop and supplying it outside the oscillation loop; and a multi-layer board for mounting the amplifier, surface acoustic wave element, phase adjustment circuit, phase shifter, and equal power divider in at least two separate layers.
This enables data processing with data transmission rates of several gigabits/second to several tens of gigabits/second while preventing an increase in the mounting area. This also minimizes circuit loss and output fluctuations and realizes a stable receiving operation for the load. The communication device according to the invention comprises an access control part for controlling data access; an oscillator for generating synchronous clocks; a PLL control part for controlling frequencies based on the outputs from the oscillator; an encoder for combining and encoding parallel data from the access control part and the synchronous clocks; a serializer for converting the parallel data combined with the synchronous clocks into serial data; a laser diode for converting the serial data into optical signals; a photodiode for converting the optical signals into electric signals; a clock data recovery for extracting the data and synchronous signals from the electric signals; a voltage controlled oscillator for providing signals to operate the clock data recovery; a deserializer for converting serial data that are extracted by the clock data recovery into parallel data; and a decoder for decoding and supplying the parallel data to the access control part, characterized by the voltage controlled oscillator comprising an amplifier; a surface acoustic wave element for forming a feedback circuit for the amplifier; a phase adjustment circuit consisting of a filter and interposed in the feedback circuit; a phase shifter consisting of a hybrid coupler to which an additional control part is attached for changing the phase value within the oscillation loop with control voltage supplied from an external source; an equal power divider for equally distributing output power within the oscillation loop and supplying it outside the oscillation loop; and a multi-layer board for mounting the amplifier, surface acoustic wave element, phase adjustment circuit, phase shifter, and qui-distributor in at least two separate layers.
This enables gigabits network systems that ensure stable circuit operation for the load while preventing an increase in the mounting area.